Semiconductor light emitting device and fabrication method thereof

ABSTRACT

Semiconductor light emitting devices and methods of producing same are provided. The semiconductor light emitting devices include a substrate that has a surface including a difference-in-height portion composed of, for example, a wurtzite compound. A crystal growth layer is formed in the substrate surface wherein at least a portion of which is oriented along an inclined plane with respect to a principal plane of the substrate. The semiconductor device includes a first conductive layer, an active layer and a second conductive layer formed on the crystal layer in a stacked arrangement and oriented along the inclined place.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent Document No.P2000-381249 filed on Dec. 15, 2000 herein incorporated by reference tothe extent permitted by law. The present application is a continuationapplication of U.S. patent application Ser. No. 10/024,883 filed on Dec.17, 2001, the disclosure of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to semiconductor devices. Morespecifically, the present invention relates to semiconductorlight-emitting devices and processes for producing same.

It is known that semiconductor light emitting devices can be fabricatedby forming a low temperature buffer layer overall on a sapphiresubstrate, forming an n-side contact layer made from GaN doped with Sithereon, and stacking an n-side cladding layer made from GaN doped withSi, an active layer made from InGaN doped with Si, a p-side claddinglayer made from AlGaN doped with Mg, and a p-side contact layer madefrom GaN doped with Mg thereon. As commercial products of semiconductorlight emitting devices having such a structure, light emitting diodesand semiconductor lasers for emitting light of blue and green having awavelength of 450 nm to 530 nm have been fabricated on a large scale.

With respect to growing gallium nitride (GaN), a sapphire substrate hasbeen often used; however, in this case, dislocations may be contained inthe grown crystal at a high density because of mismatching in latticebetween the sapphire substrate and the gallium nitride to be grownthereon. From this viewpoint, a technique for forming a low temperaturebuffer layer on a substrate is effective to suppress defects caused inthe crystal to be grown on the substrate. Further, a method of reducingcrystal defects by usual epitaxial growth in combination with epitaxiallateral overgrowth (ELO) has been disclosed in Japanese Patent Laid-openNo. Hei 10-312971.

Japanese Patent Laid-open No. Hei 10-312971 regarding a method offabricating a semiconductor light emitting device describes thatthrough-dislocations propagated in the direction perpendicular to asubstrate principal plane is deflected in the lateral direction by afacet structure formed in a growth region during fabrication of thedevice, so that it is possible to block the propagation of thethrough-dislocation and hence to reduce crystal defects.

A light emitting system including a plurality of semiconductor lightemitting devices in the form of light emitting diodes or semiconductorlasers is usable for an image display unit by using, as each of pixelsarrayed in a matrix, a combination of light emitting diodes orsemiconductor lasers of blue, green, and red, and independently drivingthe pixels; and is also usable for a white light emitting unit or anillumination unit by making the light emitting devices of blue, green,and red simultaneously emit light of blue, green, and red. Inparticular, since a light emitting device using a nitride semiconductorhas a band gap energy ranging from about 1.9 eV to about 6.2 eV, it canrealize a full-color display only by using one material. For thisreason, a multi-color light emitting device using a nitridesemiconductor has been actively studied. It is to be noted that the term“nitride” used herein means a compound which contains one or more of B,Al, Ga, In, and Ta as group III elements and N as a group V element, andwhich may contain impurities in an amount of 1% or less of the totalamount or 1×10²⁰ cm³ or less.

A technique of forming a multi-color light emitting device on the samesubstrate has been known, wherein a plurality of regions for emittinglight of respective colors, which include active layers having differentband gap energies corresponding to different emission wavelengths, arestacked, and a common electrode on the substrate side is provided whileelectrodes on the other side are individually provided on the lightemission regions. In another known multi-color light emitting device,the regions for emitting light of respective colors are stepwise formedon the substrate for easy extraction of electrodes therefrom. Themulti-color light emitting device of this type in which a plurality oflayers including a pn-junction are stacked has a possibility that thelight emission regions in the same device act just as a thyristor, andto prevent such operation similar to that of a thyristor, a multi-colorlight emitting device, in which grooves are formed between one andanother of the stepwise light emission regions for isolating the lightemission regions from each other, has been disclosed, for example, inJapanese Patent Laid-open No. Hei 9-162444.

Further, a light emitting device disclosed in Japanese Patent Laid-openNo. Hei 9-92881 is configured such that, to realize multi-color lightemission, an InGaN layer is formed on an alumina substrate via an AlNbuffer layer, wherein a portion of the InGaN layer is doped with Al toform a blue light emission region, another portion of the InGaN layer isdoped with P to form a red light emission region, and a non-dopedportion of the InGaN layer is taken as a green light emission region.

The above-described techniques, however, have the following problems.Known epitaxial lateral overgrowth techniques and known crystal growthmethods characterized by forming a facet structure in a growth regionare advantageous in that since the propagation of through-dislocationscan be deflected by a facet structure portion or the like, crystaldefects can be significantly reduced. However, to form a light emissionregion including an active layer after epitaxial lateral overgrowth orformation of the facet structure, the epitaxial lateral overgrowth isfurther performed or the facet structure is buried so as to obtain aflat plane on which the light emission region is to be formed, with aresult that the number of processing steps is increased and a timerequired for fabricating the device is prolonged.

Known multi-color light emitting devices are disadvantageous in thatsince the processing steps become complicated, it fails to form thelight emitting device at a high accuracy, and since the crystallinity isdegraded, it fails to provide good light emission characteristic. Forthe multi-color light emitting device in which grooves are formedbetween one and another of the stepwise light emission regions forisolating the light emission regions from each other, anisotropicetching must be repeated by several times for isolating the lightemission regions including active layers from each other. This causesproblems that since the crystallinity of each of the substrate and thesemiconductor layer may be degraded by dry etching, it is difficult tosustain desirable crystallinity, and that since etching is repeated byseveral times, the number of steps required for mask alignment andetching is increased.

For the multi-color light emitting device in which impurities areselectively doped in the single active layer formed on the substrate,since a margin must be provided for forming an opening portion in themask layer, a sufficient distance must be set between one and another ofthe different light emission regions, particularly, in the case ofpreviously estimating a fabrication error, so that it is difficult toform a micro-side light emitting device, and further, the number ofsteps is increased by selective doping.

SUMMARY OF THE INVENTION

An advantage of the present invention is to provide a semiconductorlight emitting device capable of reducing occurrence of crystal defectssuch as through-dislocations without increasing the number offabrication steps and to provide a method of fabricating thesemiconductor light emitting device.

Another advantage of the present invention is to provide a semiconductorlight emitting device including light emission regions having differentemission wavelengths, which is allowed to be fabricated at a highaccuracy with a reduced number of steps and which is excellent incrystallinity, and to provide a method of fabricating the semiconductorlight emitting device.

In an embodiment of the present invention, there is provided asemiconductor light emitting device including: a first conductivecladding layer, an active layer, and a second cladding layer; wherein adifference-in-height portion is formed in a surface of a wurtzite-typecompound semiconductor layer; a crystal growth layer having an inclinedplane is formed by crystal growth on the surface, having thedifference-in-height portion, of the compound semiconductor layer; andthe first conductive cladding layer, the active layer, and the secondconductive layer are sequentially formed on the crystal growth layer insuch a manner as to be approximately in parallel to the inclined planeof the crystal growth layer.

In an embodiment of the present invention, there is provided a method offabricating a semiconductor light emitting device, including the stepsof: forming a wurtzite-type compound semiconductor layer on a substrateprincipal plane in such a manner that a difference-in-height portion isformed in a surface of the compound semiconductor; forming a crystalgrowth layer having an inclined plane inclined with respect to thesubstrate principal plane by crystal growth on the surface, having thedifference-in-height portion, of the compound semiconductor layer; andstacking a first conductive cladding layer, an active layer, and asecond conductive layer in a region extending in parallel to theinclined plane.

With these configurations of the semiconductor light emitting device andthe method of fabricating the semiconductor light emitting deviceaccording to the present invention, since a wurtzite type compoundsemiconductor layer having a difference-in-height portion is formed on asubstrate principal plane, a crystal growth layer having a facetstructure can be formed by making use of a difference in crystal growthrate between crystal growth directions at the difference-in-heightportion. Since such a facet structure has an inclined plane inclinedwith respect to the substrate principal plane, it is possible tosufficiently reduce occurrence of crystal defects such asthrough-dislocations at the inclined plane. The stacked structure of afirst conductive cladding layer, an active layer, and a secondconductive cladding layer functions as a light emission region byinjecting a current thereto. In particular, according to the presentinvention, since the inclined plane inclined with respect to thesubstrate principal plane is utilized while being left as not buried, itis possible to reduce occurrence of dislocations, and to facilitate thefabrication process because of elimination of the need of burying theinclined plane.

To achieve the second object, according to a third aspect of the presentinvention, there is provided a semiconductor light emitting deviceincluding: a first conductive cladding layer, an active layer, and asecond active cladding layer; wherein a wurtzite-type compoundsemiconductor layer is formed on a substrate principal plane in such amanner that a difference-in-height portion is formed in a surface of thecompound semiconductor; a crystal growth layer having an inclined planeinclined with respect to the substrate principal plane is formed bycrystal growth on the surface, having the difference-in-height portion,of the compound semiconductor layer; the first conductive claddinglayer, the active layer, and the second conductive layer aresequentially formed on two or more crystal planes including the inclinedplane of the crystal growth layer, to form light emission regions; andelectrodes are independently formed in the light emission regions formedon the two or more crystal planes.

With this configuration of the semiconductor light emitting deviceaccording to the present invention, a first conductive cladding layer,an active layer, and a second conductive layer are sequentially formedon two or more crystal planes including an inclined plane of a crystalgrowth layer, to form light emission regions; and electrodes areindependently formed in the light emission regions formed on the two ormore crystal planes. Since the independent electrodes are formed, thelight emission regions are independently operated by supplying separatesignals to the independent electrodes. As a result, light can beindependently emitted from the two light emission regions of one device,and since light having different wavelengths can be emitted from thelight emission regions of one device, the device can be used as amulti-color light emitting device.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A to 1G are sectional views showing steps of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention. FIG. 1A illustrates the step of forming a GaN layerdoped with Si. FIG. 1B shows the step of forming a mask layer. FIG. 1Cshows the step of forming difference-in-height portions. FIG. 1D showsthe step of forming facet structures each having inclined planes. FIG.1E shows the step of forming a GaN layer doped with Mg. FIG. 1F showsthe step of forming an n-side electrode. FIG. 1G shows the step offorming a p-side electrode.

FIGS. 2A to 2G are sectional views showing steps of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention. FIG. 2A shows the step of forming a GaN layer dopedwith Si. FIG. 2B shows the step of forming a mask layer. FIG. 2C showsthe step of forming difference-in-height portions. FIG. 2D shows thestep of forming facet structures each having inclined planes. FIG. 2Eshows the step of forming a GaN layer doped with Mg. FIG. 2F shows thestep of forming an n-side electrode. FIG. 2G shows the step of forming ap-side electrode.

FIG. 3 is a perspective view showing a step of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention, wherein a facet structure is shown in a developmentstate that has a honeycomb-type inverse-hexagonal shape.

FIGS. 4A and 4B are views showing portions of the semiconductor lightemitting device according to an embodiment of the present invention.FIG. 4A shows a planar shape of a difference-in-height portion. FIG. 4Bshows a cross-sectional shape of a facet.

FIGS. 5A to 5F are sectional views showing steps of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention. FIG. 5A shows the step of forming a silicon oxidelayer. FIG. 5B shows the step of forming an opening portion in a resistlayer. FIG. 5C shows the step of forming a window portion in the siliconoxide layer. FIG. 5D shows the step of forming an electrode by alift-off process. FIG. 5E shows the step of removing the resist layer.FIG. 5F shows the step of forming an n-side electrode.

FIGS. 6A to 6D are sectional views showing steps of fabricating asemiconductor light emitting device according to an embodiment of thepresent invention. FIG. 6A shows the step of forming a silicon oxidelayer. FIG. 6B shows the step of forming an opening portion in a resistlayer. FIG. 6C shows the step of forming an electrode by a lift-offprocess. FIG. 6D shows the step of forming an n-side electrode.

FIG. 7 is a sectional perspective view showing a semiconductor lightemitting device according to an embodiment of the present invention.

FIG. 8 is a sectional perspective view showing a semiconductor lightemitting device according to an embodiment of the present invention.

FIG. 9 is a sectional perspective view showing an example of a lightemission state of the semiconductor light emitting device according toan embodiment of the present invention.

FIG. 10 is a sectional perspective view showing a semiconductor lightemitting device according to an embodiment of the present invention.

FIG. 11 is a sectional perspective view showing a semiconductor lightemitting device according to an embodiment of the present invention.

FIG. 12 is a sectional view showing a semiconductor light emittingdevice according to an embodiment of the present invention, wherein thedevice is connected to a current quantity adjusting circuit.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to semiconductor devices. In particular,the present invention relates to semiconductor light emitting devicesand methods of producing same.

In an embodiment, a semiconductor light emitting device includes awurtzite-type compound semiconductor layer having in its surface adifference-in-height portion is formed on a principal plane of asubstrate; a crystal growth layer including a facet structure having aninclined plane inclined with respect to the principal plane of thesubstrate wherein the crystal growth layer is formed by crystal growthon the surface, having the difference-in-height portion, of the compoundsemiconductor layer; and a first conductive cladding layer, an activelayer, and a second conductive cladding layer are formed in a regionextending in parallel to the inclined plane.

It should be appreciated that any suitable type of material or materialscan be utilized to fabricate the semiconductor light emitting device ofthe present invention to the extent that a wurtzite-type compoundsemiconductor layer can be formed on the substrate. For example, thesubstrate may be made from a sapphire (Al2O3, whose desirable crystalplane is an A-plane, R-plane, or C-plane), SiC (having a structure of6H, 4H or 3C), GaN, Si, ZnS, ZnO, AlN, LiMgO, LiGaO2, GaAs, MgAl2O4,InAlGaN-like or combination thereof. The substrate can be formed intoany suitable shape or configuration. In an embodiment, the substitutematerial includes a hexagonal system, cubic system or the like,preferably a hexagonal system. For example, in the case of growing agallium nitride (GaN) based compound semiconductor on a substrate, itmay be desirable that the substrate be made from sapphire with itsC-plane taken as a principal plane of the substrate. It is to be notedthat the crystal plane of sapphire used for the substrate principalplane is not strictly limited to the C-plane but may be substantiallyequivalent to the C-plane. For example, the substrate principal planemay be positioned relative to the C-plane at an angle ranging from about5° to about 6°.

A compound semiconductor layer to be formed on the substrate principalplane may be made from a nitride semiconductor having a wurtzite-typecrystal structure, a BeMgZnCdS based semiconductor layer, a BeMgZnCdObased compound semiconductor layer or the like because a facet structurewill be formed thereon in the subsequent step.

As the above nitride semiconductor having a wurtzite-type crystalstructure, there may be used a group III based compound semiconductor,for example, a gallium nitride (GaN) based compound semiconductor, analuminum nitride (AlN) based compound semiconductor, an indium nitride(InN) based compound semiconductor, an indium gallium nitride (InGaN)based compound semiconductor aluminum gallium nitride (AlGaN) basedcompound semiconductor or the like. In particular, a gallium nitridebased compound semiconductor is preferably used as the material forforming the nitride semiconductor layer to be formed on the substrate.It is to be noted that a nitride semiconductor such as InGaN, AlGaN, orGaN is not necessarily composed of only a ternary or binary mixedstructure. For example, an InGaN semiconductor may contain an impuritysuch as a trace of Al in a range not changing the function of InGaN. Inthis specification, the term “nitride” means a compound which containsone or more of B, Al, Ga, In, and Ta as the group III elements and N asthe group V element, and which may contain impurities in an amount of 1%of the total amount or less or 1×10²⁰ cm³ or less.

The compound semiconductor layer may be grown on the substrate by one ofvarious vapor phase growth processes, for example, a metal organicchemical deposition (MOCVD), metal organic vapor phase epitaxial growth(MOVPE) process, a molecular beam epitaxial growth (MBE) process, ahydride vapor phase epitaxial growth (HVPE) process or the like. In anembodiment, the MOVPE process is preferred as it is capable of growingthe compound semiconductor layer with a high crystallinity on thesubstrate at a high processing rate. In the MOVPE process, typically, analkyl metal compound is used as each of Ga, Al and In sources, forexample, TMG (trimethyl gallium), TEG (triethyl gallium), or the like,is used as the Ga source, TMA (trimethyl aluminum), TEA (triethylaluminum), or the like, is used as the Al source, and TMI (trimethylindium), TEI (triethyl indium), or the like, is used as the In source.The MovPE process can also include a gas such as ammonia or hydradine asa nitrogen source; silane gas as an Si (impurity) source, Cp2Mg(cyclopentadienyl magnesium) as a Mg (impurity) source, a DEZ (diethylzinc) gas as a Zn (impurity) source or the like. According to the MOVPEprocess, for example, an InAlGaN based compound semiconductor layer canbe grown on the substrate by supplying gases composed of In, Al, Ga andN sources and/or a gas as an impurity source to the front surface of thesubstrate heated, for example, at 600° C. or more, to decompose thesource gases, thereby allowing epitaxial growth of an InAlGaN basedcompound semiconductor on the substrate.

In an embodiment, to form a facet structure having an inclined planeinclined with respect to the substrate principal plane by crystalgrowth, a difference-in-height portion is formed in a surface of theabove-described compound semiconductor layer as an under layer forcrystal growth. The difference-in-height portion functions to make,during crystal growth, a growth rate of a crystal plane perpendicular toa crystal plane appearing on the substrate. For example, the substrateprincipal plane different from a growth rate of a crystal plane parallelto the substrate principal plane, to thereby form a facet structure. Inan embodiment, the difference-in-height portion is formed in the surfaceof the compound semiconductor layer by photolithography and anisotropicetching using a mask layer made from silicon oxide or silicon nitride.The shape of the difference-in-height portion is not particularlylimited insofar as the difference-in-height portion allows formation ofa facet structure having an inclined plane inclined with respect to thesubstrate principal plane. For example, the difference-in-height may beformed into a shape selected from a stripe shape, rectangular shape, around shape, a polygonal shape such as a triangular shape or hexagonalshape, or the like. The shape of the difference-in-height portion meansthe planar shape of the difference-in-height portion. For example,according to an embodiment of the present invention, thedifference-in-height portion having a triangular shape means not onlythe difference-in-height portion projecting into a triangular hole butalso the difference-in-height portion recessed into a triangular shape.A plurality of different-in-height portions may be formed overall orpartially on the surface of a compound semiconductor layer. In addition,different difference-in-height portions may be formed in combination.

After the difference-in-height portion is formed in the compoundsemiconductor layer, a crystal growth layer including a facet structurehaving an inclined plane is formed thereon by crystal growth inaccordance with the same manner as that for forming the above-describedcompound semiconductor layer, for example, one of various vapor phasegrowth processes, such as the metal organic chemical deposition (MOCVD)or metal organic vapor phase epitaxial growth (MOVPE) process, themolecular beam epitaxial growth (MBE) process, or the hydride vaporphase epitaxial growth (HVPE) process. The crystal growth layer formedon the compound semiconductor layer having the difference-in-heightportion is typically made from the same material as that for forming thecompound semiconductor layer. The material for forming the crystalgrowth layer, however, may be made from another compound semiconductormaterial insofar as it can form a facet structure by crystal growthwhile being dependent on the shape of the difference-in-height portion.

As previously discussed, the crystal growth layer includes a facetstructure having an inclined plane inclined with respect to a substrateprincipal plane by crystal growth. In an embodiment, the inclined planeincludes an S-plane, a {11-22} plane, the like, or planes beingsubstantially equivalent thereto. Here, the plane being substantiallyequivalent to the S-plane means a plane inclined with respect to theS-plane at an angle ranging from about 5° to about 6°. For example, ifthe C-plane is selected as the substrate principal plane, it is possibleto form the S-plane and the plane being substantially equivalentthereto. The S-plane is a stable plane which can be selectively grown onthe C+ plane. The S-plane is expressed by a (1-101) plane in Millerindex for the hexagonal system. The C+ plane and C− plane are present asthe C-plane, and similarly, the S+ plane and S− plane are present as theS-plane. According to the present invention, unless otherwise specified,the S+ plane, which is grown on the C+ plane of the GaN layer, is takenas the S-plane. In this regard, the S+ plane is more stable than the S−plane. In addition, the C+ plane is expressed by a (0001) plane inMiller index.

In the case of growing a gallium nitride based compound semiconductorfor forming the above-described crystal growth layer, the number ofbonds of gallium to nitride at the S-plane becomes two or three, whichis the largest among crystal planes excluding the C− plane. Here, sincethe C− plane cannot be formed on the C+ plane, the number of bonds ofgallium to nitride at the S-plane becomes largest among the crystalplanes. For example, in the case of growing a wurtzite-type nitride on asapphire substrate using the C+ plane as the principal plane, thesurface of the nitride generally becomes the C+ plane; however, theS-plane can be stably formed by making use of selective growth. At aplane parallel to the C+ plane, nitrogen liable to be eliminated isbonded to gallium via a single bond. On the other hand, at an inclinedS-plane, nitrogen is bonded to gallium via at least one or more bonds.In this regard, at the S-plane, a V/III ratio is effectively increased,to improve the crystallinity of the crystal growth layer. Further, inthe case of forming the crystal growth layer, it is grown along thedirection different from the orientation of the C+ plane of thesubstrate. In this regard, since dislocations propagated upwardly fromthe substrate are deflected, it is possible to reduce occurrence ofcrystal defects.

It should be appreciated that the type of an inclined plane of a facetstructure formed on the crystal growth layer is controlled, for example,on the basis of a growth condition at the time of crystal growth, andshapes of a difference-in-height portion and a mask portion. Forexample, in the case where a difference-in-height portion extending in astripe shape is formed in a surface of a gallium nitride-basedsemiconductor layer where the longitudinal direction of the stripe is a<11-20> direction, a facet structure having the S-plane as an inclinedplane is formed. In this case, the facet structure is formed into aninverse V-shape in a cross-sectional view taken along a planeperpendicular to the longitudinal direction of the stripe. Since theshape of the difference-in-height portion is not limited to the stripeshape, the cross-section of the crystal growth layer can have any othershape than the stripe shape, for example, a rectangular shape, a roundshape, a triangular shape, a hexagonal shape, or the like. The crystalgrowth layer is grown depending on the shape of the difference-in-heightportion. If the extending direction of an end portion of thedifference-in-height portion is set to be approximately perpendicular toa <1-100> direction or the <11-20> direction, then a difference ingrowth rate between growth in the lateral direction and growth in thevertical direction appears necessarily results in a facet structure. Inan embodiment, crystal growth temperature at the time of growth of thecrystal growth layer is about 1100° C. or less. If the crystal growthtemperature is higher than 1100° C., there occurs an inconvenience thatcharacteristics (particularly, optical characteristic) of the crystal isdegraded. In an embodiment, a pressure at the time of growth of thecrystal growth layer is about 100 Torr or more. If the pressure is lessthan 100 Torr, there occurs an inconvenience that the growth conditionis varied, so that a desired crystal plane cannot be obtained and aconductivity of the crystal growth layer becomes poor.

In one embodiment, the semiconductor device of the present inventionincludes a first conductive cladding layer, an active layer, and asecond conductive cladding layer stacked on the crystal growth layerhaving the facet structure in a region extending in parallel to theinclined plane of the facet structure. In an embodiment, a crystalgrowth temperature at the time of growth of an InGaN active layer is setin a range of about 700° C. to about 800° C. At such a crystal growthtemperature, since a decomposition efficiency of ammonia is low, theamount of an N source must be increased. As a result of observing afacet structure grown on a crystal growth layer by using cathodeluminescence in an experiment performed by the inventors, it wasrevealed that the S-plane taken as an inclined plane of the facetstructure has a desirable crystallinity and exhibits a higher luminousefficiency as compared with the C+ plane. As a result of observation ofthe surface of the inclined plane by AFM, it was found that the surfacewas suitable for incorporation of InGaN.

It was also found that the growth of the S-plane allows the layer dopedwith Mg to be grown in a good surface state and makes a doping conditionfor the layer doped with Mg very different from a doping condition forthe layer doped with Mg formed on the C+ plane. As a result ofmicroscopic photoluminescence mapping, although the surface of the layerdoped with Mg formed on the C+ plane by the usual manner has anunevenness of a pitch of about 1 μm, the surface of the layer doped withMg formed on the S-plane obtained by selective growth was even andmeasured at a resolution of about 0.5 mm to about lam. Further, as aresult of observation by SEM, it was revealed that the flatness of theinclined plane, that is, the S-plane is superior to that of the C+plane.

With respect to the first conductive cladding layer, the active layer,and the second conductive cladding layer, which are layered in a stackedarrangement in the region extending in parallel to the inclined plane,the conductive type of the first conductive cladding layer is a p-typeor an n-type, and the conductive type of the second conductive claddinglayer is the n-type or the p-type. For example, in the case where acrystal growth layer having the S-plane is made from a gallium nitridebased compound semiconductor doped with silicon, a gallium nitride basedcompound layer doped with silicon may be formed as an n-type claddinglayer on the compound semiconductor layer having the S-plane, an InGaNlayer can be formed as an active layer thereon, and a gallium nitridebased compound semiconductor layer doped with magnesium be formed as ap-type cladding layer thereon, to thus form a double hetero structure.The active layer may be of a structure in which an InGaN layer is heldbetween AlGaN layers or an AlGaN layer is provided on one side of theInGaN layer. The active layer may be a single bulk active layer;however, it may be of a quantum well structure such as a single quantumwell (SQW) structure, a double quantum well (DQW) structure, or amulti-quantum well (MQW) structure. In the case of adopting the quantumwell structure, one or more barrier layers are used for separatingquantum wells from each other.

The use of the InGaN layer as the active layer is advantageous infacilitating the fabricating process and enhancing an emissioncharacteristic of the device. Another advantage of the use of the InGaNlayer is that the InGaN layer can be easily crystallized on the S-plane,which has the structure from which nitrogen atoms are less eliminated,with a good crystallinity to enhance the emission efficiency. Inaddition, even in a state that a nitride semiconductor is not doped withan impurity, the conductive type of the nitride semiconductor becomesthe n-type because of nitrogen holes generated in crystal; however, ingeneral, an n-type nitride semiconductor having a desirable carrierconcentration is obtained by doping a doner impurity such as Si, Ge, Se,or the like, in crystal. On the other hand, a p-type nitridesemiconductor is obtained by doping an acceptor impurity such as Mg, Zn,C, Be, Ca, Ba, or the like, in crystal. In this case, to obtain a p-typenitride semiconductor having a high carrier concentration, the nitridesemiconductor having been doped with an acceptor impurity may beannealed in an inert gas atmosphere such as nitrogen or argon, oractivated by irradiation of electron beams, microwaves, or light. Suchan active layer is desirable to be obtained by a semiconductor growthlayer formed only one growth. Only one growth means growth by a singlefilm formation treatment or a sequence of film formation treatments, andtherefore, it does not mean repeated formation of a plurality of activelayers.

As previously discussed, the first conductive cladding layer, the activelayer, and the second conductive cladding layer extend within a planeparallel to an inclined plane. Such formation of the stacked structurewithin a plane parallel to an inclined plane can be easily performed bycontinuing crystal growth, after formation of the inclined plane. Thefirst conductive cladding layer can be made from the same materialhaving the same conductive type as that of the crystal layer having theS-plane, and accordingly, after the crystal layer having the S-plane isformed, the same material can be continuously grown by adjusting aconcentration thereof. Alternatively, there may be adopted a structurethat part of the crystal layer having the S-plane functions as the firstconductive cladding layer.

According to the semiconductor light emitting device of the presentinvention, inventors have discussed that the luminous efficiency can beenhanced by making use of a good crystallinity of an inclined planeformed by crystal growth. In particular, when a current is injected onlyin the S-plane having a good crystallinity, the luminous efficiency canbe made higher because the S-plane has a high In capture characteristicand a good crystallinity. In this regard, to fabricate a multi-colorlight emitting device by using an InGaN layer, it is desirable that Incan be sufficiently captured as crystal, and the luminous efficiency ofthe device can be enhanced by making use of a good crystallinity of theS-plane. In the case of crystal growth on the C+ plane, gallium has onlyone bond to nitrogen liable to be eliminated, and accordingly, whencrystal growth is performed by using ammonia whose decompositionefficiency is low, it is impossible to increase an effective V/IIIratio, with a result that it fails to obtain good crystal growth. In thecase of crystal growth on the S-plane, since the number of bonds ofgallium to nitrogen at the S-plane is as large as two or three, theelimination of nitrogen becomes small and thereby the effective V/IIIratio becomes high. In general, the quality of crystal grown on not onlythe S-plane but also any plane other than the C+ plane becomes highbecause the number of bonds of gallium to nitrogen tends to be increasedfor growth on any crystal growth plane other than the C+ plane. Thegrowth of crystal on the S-plane is also advantageous in that the amountof In incorporated in the crystal grown on the S-plane becomes high. Theincreased amount of In incorporated in crystal grown on the S-plane iseffective for fabricating a multi-color light emitting device because aband gap energy is determined on the base of the amount of Inincorporated in crystal.

In an embodiment of the semiconductor light emitting device of thepresent invention, two or three light emission regions having two orthree kinds of emission wavelengths can be formed on the same device.These light emission regions are formed on two or more crystal planesincluding an inclined plane of a crystal growth layer. In the case wherethe substrate principal plane is the C-plane and the inclined plane isthe S-plane, one of the light emission regions is formed in a regionparallel to the S-plane, and another light emission region can be formedin a region of a crystal growth plane corresponding to the C-plane. Theemission wavelength of one light emission region can be made differentfrom that of another light emission region by making at least one of acomposition and a thickness of an active layer between the two lightemission regions, that is, making only the composition of the activelayer, only the thickness of the active layer, or both the compositionand the thickness of the active layer different between the two lightemission regions.

The composition of an active layer can be adjusted by changing a mixingratio of elements of a ternary or binary mixed crystal constituting theactive layer. In the case of using an InGaN layer as the active layer, asemiconductor light emitting device for emitting light of along-wavelength can be obtained by increasing the amount of In containedin the active layer. In crystal growth of an InGaN layer of anembodiment, a migration length of InGaN, particularly with respect toIn, is estimated about 1 μm to about 2 μm at about 700° C. for optimumcrystal growth of the InGaN layer having a relatively large amount ofIn. This is because InGaN precipitated on a mask is grown from aselective growth portion only by about 1 μm to about 2 μm. The migrationlength of In may be thus regarded as about 1 μm to about 2 μm. Since themigration length of In contained in InGaN in a region from the maskportion of the growth portion is relatively short, that is, about 1 μmto about 2 μm, the content of In or the thickness of InGaN may differ insuch a region.

The wavelength of light emerged from an active layer is liable to bechanged depending on from which location of the active layer the lightis emerged. This is because the migration length of In is shorten atabout 700° C. optimum for crystal growth of the InGaN layer having arelatively large amount of In. According to the semiconductor lightemitting device of the present invention, by making effective use of thefact that the emission wavelength differs between one and another ofregions within the same active layer, first and second light emissionregions having different emission wavelengths are formed in the sameactive layer, and currents are injected in the first and second lightemission regions, respectively. Independent electrodes are formed in thefirst and second light emission regions for independently injectingcurrents therein. In this case, the electrodes on one side (p-side orn-side) in the first and second light emission regions can be utilized.According to an embodiment of the present invention, a multi-colorsemiconductor light emitting device can be obtained by forming two ormore light emission regions having different emission wavelengths in thesame active layer, and independently injecting current therein, andfurther, a semiconductor light emitting device for emitting light of amixed color or white light can be obtained by forming two or more lightemission regions having different emission wavelengths in the sameactive layer, and controlling the device such that the light emissionregions simultaneously emit light.

In a crystal layer formed on a facet structure having an inclined plane,an effective V/III ratio is determined by a complicated combination of alocation, orientation of a crystal plane, and the like. The growth ofthe facet is also dependent on growth conditions such as a growthtemperature. From experimental data obtained by examining cathodeluminescence of a double hetero structure produced by selective growthin accordance with an embodiment of the present invention, it wasrevealed that the emission wavelength of an upper portion of the doublehetero structure is longer than that of a lower portion of the doublehetero structure by about 100 (nanometers) nm. These experimental datashowed that, by providing different electrodes at different locations ofthe double hetero structure, two or more light emission regions havingdifferent emission wavelengths can be provided with respect to a singlecrystal growth, and therefore, a semiconductor light emitting device foremitting light of multi-colors or emitting white light can be fabricatedvia a single crystal growth.

For example, in the case of forming a stripe shaped difference-in-heightportion and forming a facet structure having an inclined plane composedof the S-plane obtained by crystal growth and the C-plane, a lightemission region formed on the inclined plane is taken as along-wavelength light emission region and a light emission region formedon the C-plane is taken as a short-wavelength light emission region.This may be reversed depending on the crystal growth conditions. Also,since the incorporated amount of In differs depending on a distance froma substrate, an emission wavelength in a higher light emission regionparallel to the C-plane becomes different from an emission wavelength ina lower light emission region parallel to the C-plane. As a result, itis possible to provide a first light emission region on the S-plane, asecond light emission region on a higher plane parallel to the C-plane,and a third light emission region on a lower plane parallel to theC-plane.

Electrodes for independently injecting currents in such light emissionregions having different emission wavelengths are individually formed inthese light emission regions. In this case, the electrodes on one side(p-side or n-side) can be utilized. To lower a contact resistance, acontact layer may be formed, and then an electrode be formed thereon. Ingeneral, each electrode is obtained by forming a multi-layer metal filmby vapor-deposition. Such a multi-layer metal film may be finely dividedinto electrodes for respective light emission regions byphotolithography and lift-off, or the like. Each electrode may be formedon a selective crystal growth layer or one surface of a substrate;however, to realize electrode wiring at a high density, electrodes maybe provided on both the sides. Electrodes provided in different regionsand independently driven may be formed from the same electrode materialby photolithography and lift-off, or the like; however, they may be madefrom different and suitable electrode materials. A thickness of a resistlayer used for lift-off is preferably in a range of about 1 μm or more.If the thickness of the resist layer is less than about 1 μm, it isdifficult to smoothly perform the lift-off and hence to effectivelyremove the useless metal film.

Currents may be independently injected in respective light emissionregions having different emission wavelengths. In an embodiment, thesemiconductor light emitting device of the present invention, which caninclude a structure including a plurality of emission regions foremitting light of RGB (red (R), green (G), blue (B)) or CYM (cyan (C),yellow (Y), magenta (M)), is applicable for a color image display suchas a full color display. Further, the semiconductor light emittingdevice of the present invention in accordance with an embodiment whichhas a structure including a plurality of light emission regions foremitting light of three primary colors or two or more colors, isapplicable for an illuminating unit, or the like, for emitting light ofa mixed color or white light by injecting the same current in theplurality of light emission regions.

By way of example, and not limitation, the following examples illustratea variety of semiconductor light emitting devices in accordance with anembodiment of the present invention.

EXAMPLE ONE

A semiconductor light emitting device is fabricated by forming aplurality of stripe shaped difference-in-height portions on a sapphiresubstrate, and forming a crystal growth layer having facet structureseach having inclined planes by making use of the stripe shapeddifference-in-height portions. A method of fabricating the semiconductorlight emitting device and a device structure thereof according to anembodiment will be described with reference to FIGS. 1A to 1G.

As shown in FIG. 1A, a GaN layer 11 doped with silicon is formed atabout 1000° C. on a principal plane (C+ plane) of a sapphire substrate10. In addition, a low temperature buffer layer (not shown) made fromAlN or GaN is often formed at a low temperature of about 500° C. betweenthe sapphire substrate 10 and the GaN layer 11. It should be appreciatedthat the layers of the semiconductor device of the present invention canbe grown under any suitable operating conditions, such as pressuresvarying from about 200 Torr or more, including about 740 Torr or atabout standard or normal pressures.

As shown in FIG. 1B, a mask layer 12 made from SiO2 or SiN is formedoverall on the GaN layer 11 doped with silicon to a thickness of about100 nm to about 500 nm. The mask layer 12 is patterned, byphotolithography and etching using a photoresist layer, into a patternhaving stripe shaped opening portions 13 spaced parallel from each otherwith a specific pitch. The depth of each opening portion 13 is set suchthat the opening portion 13 reaches the GaN layer 11. For example, eachstripe shaped opening portion 13 extends in the <11-20> or <1-100>direction, and a width of the opening portion 13 is in a range of about0.1 μm to about 10 μm. After the opening portions 13 are formed in themask layer 12, the resist layer is removed. In this state, the GaN layer11 is exposed within the opening portions 13 formed in the mask layer12.

A surface of the GaN layer 11 is selectively etched by using the masklayer 12 as a mask, so that the surface of the GaN layer 11 isselectively cut off in a pattern depending on the pattern of the stripeshaped opening portions 13, to form stripe shaped difference-in-heightportions 14. The difference-in-height portion 14 has a high-levelportion which is located directly under a mask portion of the mask layer12 and is thereby not etched, and a low-level portion which is locatedunder the opening portion 13 and is thereby etched. In a plan view, thestripe pattern of the difference-in-height portions 14 corresponds tothe stripe pattern of the opening portions 13 of the mask layer 12.After the difference-in-height portions 14 are formed, the mask layer 12is removed by hydrofluoric acid or the like. Such a state is shown inFIG. 1C.

As shown in FIG. 1D, GaN doped with Si is grown on the surface, havingthe difference-in-height portions 14, of the GaN layer 11 by epitaxialgrowth, to form a crystal growth layer 15 including facet structures 17each having inclined planes. The epitaxial growth may be performed,after the substrate temperature is raised, in accordance with a vaporphase epitaxial (VPE) process, an organic metal chemical vapordeposition (MOCVD), or the like. At the time of crystal growth, thereappears a facet structure having inclined planes with elapsed time dueto a difference in crystal growth rate between different planes of eachdifference-in-height portion 14. Such an inclined plane is designated byreference numeral 16 in FIG. 1D, which may be typically an S-plane, thatis, the {1-101} plane, or {11-22} plane. Depending on the shape of thestripe shaped difference-in-height portion 14, a pair of the inclinedplanes 16 are opposed to each other at the low-level portion, that is,the valley of the difference-in-height portion 14. That is to say, eachfacet structure, designated by reference numeral 17, is configured as aprojecting rib which is formed into an approximately inverse-V shape incross-section and which extends along the longitudinal direction of thestripe shape of the difference-in-height portion 14.

As shown in FIG. 1E, after the crystal growth layer 15 including thefacet structures 17 each having the inclined planes 16 is formed, a GaNlayer doped with Si is formed on the crystal growth layer 15, an InGaNlayer is formed thereon under a condition that the growth temperature islowered, and a GaN layer 18 doped with Mg is formed thereon. The GaNlayer doped with Si functions as a first conductive cladding layer, theInGaN layer functions as an active layer, and the GaN layer 18 dopedwith Mg functions as a second conductive cladding layer. It is to benoted that the GaN layer doped with Si and the InGaN layer, which areformed under the GaN layer 18 doped with Mg, are depicted by a line 19.These layers forming a light emission region, which are formed on thefacet structures 17 each having the inclined planes 16, extend inparallel to the inclined planes 16. A thickness of the InGaN layer maybe in a range of about 0.5 nm to about 10 nm, preferably, about 1 nm toabout 3 nm. The InGaN layer may be replaced with a quantum wellstructure having an (Al)GaN/InGaN structure, a multi-quantum wellstructure, a multi-structure using a GaN layer or an InGaN layer as aguide layer or other suitable structure. At this time, an AlGaN layermay be grown on the InGaN layer. In this regard, since the active layerand the cladding layers are directly formed on the facet structures 17each having the inclined planes 16, it is possible to eliminate the needof provision of a step of burying the facet structures each having theinclined planes with the GaN layer. Also in the case of using theS-planes as the inclined planes, since the number of bonds of gallium tonitrogen at the S-plane becomes larger than that at any other crystalplane, it is possible to enhance the quality of crystal.

As shown in FIG. 1F, part of the stacked layers are removed, to form anopening portion 20 reaching the GaN layer 11. A Ti/Al/Pt/Au electrode isformed by vapor deposition on a portion, exposed within the openingportion 20, of the GaN layer 11. The Ti/Al/Pt/Au electrode is taken asan n-side electrode 21 as shown in FIG. 1F.

After the n-side electrode 21 is formed, an Ni/Pt/Au electrode orNi(Pd)/Pt/Au electrode is formed by vapor deposition on the uppermostone of the stacked layers, that is, the GaN layer 18 doped with Mg. TheNi/Pt/Au electrode or Ni(Pd)/Pt/Au electrode is taken as a p-sideelectrode 22 as shown in FIG. 1G. In addition, if a transparentelectrode is formed as the p-side electrode, light can be emerged froman upper surface side of the device, and if the thickness of the p-sideelectrode is large, light can be emerged from a lower surface side ofthe device.

The semiconductor light emitting device thus fabricated has a structureshown in FIG. 1G. As described above, the GaN layer 11 doped withsilicon is formed on the sapphire substrate 10 with the C+ plane ofsapphire taken as the substrate principal plane; the facet structures 17each having the inclined planes 16 which are inclined with respect tothe C+ plane by making use of the difference-in-height portions 14formed in the surface of the GaN layer 11; and the GaN layer doped withSi, the InGaN layer, and the GaN layer 18 doped with Mg are formed insuch a manner as to extend on the planes parallel to the inclined planes16. In this structure, the InGaN layer held between the two GaN layersis taken as the active layer for emitting light. When a current issupplied to the active layer between the p-side electrode 22 connectedto the GaN layer 18 doped with Mg and the n-side electrode 21 connectedto the GaN layer 11 doped with Si, there occurs light emission of thesemiconductor light emitting device having the above structure.

In the semiconductor light emitting device having the above structure,the facet structures 17 each having the inclined planes 16 are formedbefore the active layer is formed, and consequently, even ifthrough-dislocations are propagated from the substrate, the propagationof the through-dislocations is deflected by the inclined planes 16, witha result that it is possible to suppress occurrence of crystal defects.In this regard, since it is not required to bury the facet structures 17each having the inclined planes 16 with the GaN layer, it is possible toreduce the number of steps and to relatively shorten a time required forfabricating the light emitting device. Further, since the claddinglayers and the active layer are formed by making use of the inclinedplanes 16 which are inclined or diagonally oriented with respect to thesubstrate principal plane, it is possible to form a light emissionregion with good crystallinity because the number of bonds of gallium tonitrogen becomes larger at each inclined plane 16.

It should be appreciated that the semiconductor devices of the presentinvention can be applied in a variety of different and suitableapplications. For example, the semiconductor light emitting device canbe used not only as a light emitting diode but also as a semiconductorlaser by forming a resonance end face at an end portion of the device,and further, it can be used as a light emitting diode or semiconductorlaser of multi-colors by forming electrodes in two or more lightemission regions different from each other in terms of emissionwavelength as will be described.

EXAMPLE TWO

In Example Two, a semiconductor light emitting device is fabricated inthe same manner as that for fabricating the semiconductor light emittingdevice Example One except for formation of a facet structure.

As shown in FIG. 2A, a GaN layer 31 doped with silicon is formed atabout 1000° C. on a principal plane (C+ plane) of a sapphire substrate30. In addition, a low temperature buffer layer (not shown) made fromAlN or GaN can be formed at a low temperature of about 500° C. betweenthe sapphire substrate 10 and the GaN layer 31. It is to be noted that,in the fabrication process according to an embodiment, growth ofrespective layers are grown substantially at about normal or standardpressures, for example, about 740 Torr.

As shown in FIG. 2B, a mask layer 32 made from SiO2 or SiN is formedoverall on the GaN layer 31 doped with silicon to a thickness of about100 nm to about 500 nm. The mask layer 12 is patterned, byphotolithography and etching using a photoresist layer, into a patternhaving stripe shaped opening portions 33 spaced parallel from each otherwith a specific pitch. The depth of each opening portion 13 is set suchthat the opening portion 33 reaches the surface of the GaN layer 31. Forexample, each stripe shaped opening portion 33 extends in the <11-20> or<1-100> direction, and a width of the opening portion 33 is in a rangeof about 0.1 μm to about 10 μm. After the opening portions 33 are formedin the mask layer 32, similar to Example One, the resist layer isremoved. In this state, the GaN layer 31 is exposed within the openingportions 33 formed in the mask layer 32.

A surface of the GaN layer 31 is selectively etched by using the masklayer 32 as a mask, so that the surface of the GaN layer 31 isselectively cut off in a pattern depending on the pattern of the stripeshaped opening portions 33, to form stripe shaped difference-in-heightportions 34. The difference-in-height portion 34 has a high-levelportion located directly under a mask portion of the mask layer 32, anda low-level portion located under the opening portion 33. After thedifference-in-height portions 34 are formed, the mask layer 32 isremoved by hydrofluoric acid or the like. Such a state is shown in FIG.2C.

As shown in FIG. 2D, a crystal growth layer including facet structureseach having inclined planes is formed by epitaxial growth on thesurface, having the difference-in-height portions 34, of the GaN layer31. The epitaxial growth may be performed, after the substratetemperature is raised, in accordance with a vapor phase epitaxial (VPE)process, an organic metal chemical vapor deposition (MOCVD), or thelike. During crystal growth, there appears a facet structure 38 havinginclined planes 35 with elapsed time due to a difference in crystalgrowth rate between different planes of each difference-in-heightportion 34. The inclined plane 35 may be typically the {11-22} plane orthe S-plane. Depending on the shape of the stripe shapeddifference-in-height portion 34, a pair of the inclined planes 35 areopposed to each other at the low-level portion, that is, the valley ofthe difference-in-height portion 34. In accordance with this embodiment,a facet bottom surface portion 37 composed of the flat C-plane is formedbetween the pair of inclined planes 35, and a facet top surface portion36 is formed by crystal growth on the high-level portion, kept at theC-plane, of the difference-in-height portion 34.

As shown in FIG. 2E, after the crystal growth layer including the facetstructures 38 each having the inclined planes 35, the facet bottomsurface portion 37, and the facet top surface portion 36 is formed, aGaN layer doped with Si is formed on the crystal growth layer, an InGaNlayer is formed thereon under a condition that the growth temperature islowered, and a GaN layer 39 doped with Mg is formed thereon. The GaNlayer doped with Si functions as a first conductive cladding layer, theInGaN layer functions as an active layer, and the GaN layer 39 dopedwith Mg functions as a second conductive cladding layer. It is to benoted that the GaN layer doped with Si and the InGaN layer, which areformed under the GaN layer 39 doped with Mg, are depicted by a line 40in FIG. 2E. These layers forming a light emission region, which areformed on the facet structures 38 each having the inclined planes 35,extend in parallel to the inclined planes 35 and also extend in parallelto the facet bottom surface portion 37 having the C-plane and the facettop surface portion 36 having the C-plane. A thickness of the InGaNlayer may be in a range of about 0.5 nm to about 6 nm. The InGaN layermay be replaced with a quantum well structure having an (Al)GaN/InGaNstructure, a multi-quantum well structure, a multi-structure using a GaNlayer or an InGaN layer as a guide layer, or other like structure. Atthis time, an AlGaN layer may be grown on the InGaN layer. In thisregard, since the active layer and the cladding layers are directlyformed on the facet structures 38 each having the inclined planes 35, itis possible to eliminate the need of provision of a step of burying thefacet structures each having the inclined planes with the GaN layer.

As shown in FIG. 2F, like Example One, part of the stacked layers areremoved, to form an opening portion 42 reaching the GaN layer 31. ATi/Al/Pt/Au electrode is formed by vapor deposition on a portion,exposed within the opening portion 42, of the GaN layer 31. TheTi/Al/Pt/Au electrode is taken as an n-side electrode 41 as shown inFIG. 2F.

After the n-side electrode 41 is formed, like Example One, an Ni/Pt/Auelectrode or Ni(Pd)/Pt/Au electrode is formed by vapor deposition on theuppermost one of the stacked layers, that is, the GaN layer 39 dopedwith Mg. The Ni/Pt/Au electrode or Ni(Pd)/Pt/Au electrode is taken as ap-side electrode 43 as shown in FIG. 2G.

The semiconductor light emitting device thus fabricated has a structureshown in FIG. 2G. As described above, the GaN layer 31 doped withsilicon is formed on the sapphire substrate 30 with the C+ plane ofsapphire taken as the substrate principal plane; the facet structures 38each having the inclined planes 35 which are inclined with respect tothe C+ plane by making use of the difference-in-height portions 34formed in the surface of the GaN layer 31; and the GaN layer doped withSi, the InGaN layer, and the GaN layer 39 doped with Mg are formed insuch a manner as to extend on the planes parallel to the inclined planes35 and on the planes parallel to the C-plane. In this structure, theInGaN layer held between the two GaN layers is taken as the active layerfor emitting light. When a current is supplied to the active layerbetween the p-side electrode 43 connected to the GaN layer 39 doped withMg and the n-side electrode 41 connected to the GaN layer 31 doped withSi, there occurs light emission of the semiconductor light emittingdevice having the above structure.

In the semiconductor light emitting device having the above structure,the facet structures 38 each having the inclined planes 35 are formedbefore the active layer is formed, and consequently, even ifthrough-dislocations are propagated from the substrate, the propagationof the through-dislocations is deflected by the inclined planes 35, witha result that it is possible to suppress occurrence of crystal defects.In this embodiment, since it is not required to bury the facetstructures 38 each having the inclined planes 35 with the GaN layer, itis possible to reduce the number of steps and to decrease a timerequired for fabricating the light emitting device; and since thecladding layers and the active layer are formed by making use of theinclined planes 35 which are inclined with respect to the substrateprincipal plane, it is possible to form a light emission region withgood crystallinity because the number of bonds of gallium to nitrogenbecomes larger at each inclined plane 35.

As previously discussed, the semiconductor device of the presentinvention can be applied in a variety of suitable applications.

EXAMPLE THREE

A semiconductor light emitting device in accordance with an embodimentof the present invention can be fabricated by making use of a crystalgrowth layer which is formed in a pattern of inverse-hexagonal pyramidshapes overall on a substrate principal plane. As shown in FIG. 3, aperspective view of a crystal growth layer used for fabricating thesemiconductor light emitting device of an embodiment of the presentinvention is provided. Like the first and second examples, the crystalgrowth layer is obtained by forming a GaN layer 51 doped with silicon ona sapphire substrate 50, forming difference-in-height portions (notshown) in the GaN layer 51 doped with silicon, and growing a GaN layer53 doped with silicon in a pattern of inverse-hexagonal pyramid shapesas shown in FIG. 3.

As shown in FIG. 4A, a plurality of equilateral hexagonal shapedrecesses 61 are formed in a flat surface of the GaN layer 51 in such amanner that the opposed sides of the adjacent two of the recesses 61 areseparated from each other with a specific gap put therebetween like ahoneycomb pattern or are in contact with each other. To grow aninverse-hexagonal pyramid shaped crystal 63 shown in FIG. 4B, an endportion 62 of the equilateral hexagonal recess, that is, thedifference-in-height portion 61 may extend, for example, in thedirection perpendicular to the <1-100> direction or the <11-20>direction. An angle of the lowest portion of the inverse-hexagonalpyramid shape 63 can be set to about 60° by adjusting a crystal growthcondition. In this case, the crystal layer can be grown in a pattern ofinverse-equilateral hexagonal pyramid shapes. In addition, the crystallayer can be also grown in a pattern of truncated inverse-hexagonalpyramid shapes each having a bottom plane taken as the C-plane.

After the GaN layer 53 doped with silicon is formed in a pattern ofinverse-hexagonal pyramid shapes shown in FIG. 3, a GaN layer doped withSi, an InGaN layer, a GaN layer doped with Mg are sequentially stackedon the GaN layer 53. Since each inverse-hexagonal pyramid of the patternof the GaN layer 53 has inclined planes for forming a facet structure,the layers stacked thereon extend in parallel to the inclined planes.The InGaN layer held between the two GaN layers acts as an active layerfor light emission. It is to be noted that, in the fabrication processaccording to an embodiment, respective layers are grown at about normalor standard pressure, for example, about 740 Torr.

As previously discussed, the semiconduction device of the presentinvention can be applied in a variety of different and suitableapplications.

EXAMPLE FOUR

In an embodiment, an approximately V-shaped light emission region isformed by using a stripe shaped difference-in-height portion, and anelectrode is formed in the light emission region. The processing stepswill be described with reference to FIGS. 5A to 5F.

A GaN layer 71 doped with silicon is formed on a principal plane (C+plane) of a sapphire substrate 70. A low temperature buffer layer may beformed before the GaN layer 71 doped with silicon is formed. LikeExample Two, stripe shaped difference-in height portions are formed in asurface of the GaN layer 71 doped with silicon, followed by continuationof crystal growth by using the difference-in-height portions, to obtainthe GaN layer 71 having approximately V-shaped valleys 72 as shown inFIG. 5A. The approximately V-shaped valley 72 is formed by inclinedplanes opposed to each other at a specific angle. The inclined plane isselected from the S-plane, the {11-22} plane, and planes beingsubstantially equivalent thereto. Although a bottom of the valley 72 isV-shaped at a specific angle as shown, a plane parallel to the C-planemay appear on the bottom of the valley 72.

A GaN layer doped with Si, an InGaN layer 75 shown by a line in thefigure, and a GaN layer 73 doped with Mg are sequentially stacked on theGaN layer 71. The GaN layer doped with Si, the InGaN layer 75, and theGaN layer 73 doped with Mg form a light emission region. Even at eachapproximately V-shaped valley 72, the light emission region is formed bythe stacked structure of the GaN layer doped with Si, the InGaN layer75, and the GaN layer 73 doped with Mg. Subsequently, a silicon oxidelayer 74 is formed overall on the stacked structure in such a manner asto cover the inside of each approximately V-shaped valley 72. It is tobe noted that in the fabrication process, respective layers are grown atabout normal or standard pressure, for example, about 740 Torr.

After formation of the silicon oxide layer 74 overall on the stackedstructure, a resist layer 76 is formed overall on the silicon oxidelayer 74. As shown in FIG. 5B, an opening portion 77 is formed, by aphotolithography technique, in the resist layer 76 at a positioncorresponding to the approximately V-shaped valley 72 in which anelectrode is to be formed. The depth of the opening portion 77 reachesthe surface of the silicon oxide layer 74. In addition, the width of theopening portion 72 is shorter than a width of an opening of theapproximately V-shaped valley 72, so that only the inclined planes ofthe valley 72 are exposed within the opening portion 77.

A portion of the silicon oxide layer 74, located at the positioncorresponding to the approximately V-shaped valley 72, is removed by RIE(Reactive Ion Etching) or wet etching using a hydrofluoric acid basedetchant via the opening portion 77 of the resist layer 76. With thepartial removal of the silicon oxide layer 74 at the valley 72, the GaNlayer 73 doped with Mg is exposed at the valley 72. The resist layer 76is then removed and a resist layer 78 for forming an electrode by aliftoff process is formed. The resist layer 78 has a window portion 79at a position at which the surface of the GaN layer 73 is exposed. Morespecifically, as shown in FIG. 5C, a cross-sectional portion of thesilicon oxide layer 74 and the GaN layer 73 doped with Mg are exposedwithin the window portion 79 of the resist layer 78.

After the mask of the resist layer 78 and the silicon oxide layer 74 isformed, as shown in FIG. 5D, a p-side electrode material such asNi/Pt/Au or Ni(Pd)/Pt/Au is deposited via the window portion 79, to forma p-side electrode material layer 80. Since a height differenceequivalent to the total height of the resist layer 78 and the siliconoxide layer 74 lies between the top and the bottom of the window portion79, the film is thinned or not formed at the stepped portion of thewindow portion 79, whereby a p-side electrode 81 being approximatelyV-shaped in cross section is formed at the valley 72.

After the p-side electrode 81 is formed at the valley 72, as shown inFIG. 5E, the resist layer 78 on the silicon oxide layer 74 is removed(that is, lifted off) by using a solvent such as acetone, to remove thep-side electrode material layer 80 excluding the p-side electrode 81 atthe valley 72. Finally, an opening portion 82 is formed in such a manneras to reach the GaN layer 71 doped with Si, and an n-side electrode 83is formed as shown in FIG. 5F.

In accordance with the above-described fabrication steps, even when anapproximately V-shaped light emission region is formed by using a stripeshaped difference-in-height portion, the p-side electrode 81 beingapproximately V-shaped in cross-section can be formed at the valley 72in the light emission region, to allow injection of a current in thelight emission region.

EXAMPLE FIVE

In an embodiment, the semiconductor device of the present invention caninclude substantially V-shaped valleys that are formed by using stripeshaped difference-in-height portions, a light emission region that isformed in a flat portion, parallel to the C-plane, located between thevalleys, and an electrode that is formed in the light emission region.The processing steps of this example will be described with reference toFIGS. 6A to 6D.

A GaN layer 91 doped with silicon is formed on a principal plane(C+plane) of a sapphire substrate 90. A low temperature buffer layer maybe formed before the GaN layer 91 doped with silicon is formed. Like thesecond embodiment, stripe shaped difference-in height portions areformed in a surface of the GaN layer 91 doped with silicon, followed bycontinuation of crystal growth by using the difference-in-heightportions, to obtain the GaN layer 91 having approximately V-shapedvalleys 92 as shown in FIG. 6A. The approximately V-shaped valley 92 isformed by inclined planes opposed to each other at a specific angle. Theinclined plane is selected from the S-plane, the {11-22} plane, andplanes being substantially equivalent thereto. Although a bottom of thevalley 92 is V-shaped at a specific angle in this embodiment, a planeparallel to the C-plane may appear on the bottom of the valley 92.

A GaN layer doped with Si, an InGaN layer shown by a line in the figure,and a GaN layer 93 doped with Mg are sequentially stacked on the GaNlayer 91. The GaN layer doped with Si, the InGaN layer, and the GaNlayer 93 doped with Mg form a light emission region. Even at eachapproximately V-shaped valley 92, the light emission region is formed bythe stacked structure of these GaN layer doped with Si, the InGaN layer,and the GaN layer 93 doped with Mg. Subsequently, a silicon oxide layer94 is formed overall on the stacked structure in such a manner as tocover the inside of each approximately V-shaped valley 92. It is to benoted that in the fabrication process, respective layers are grown atabout normal pressure, for example, about 740 Torr.

After formation of the silicon oxide layer 94 overall on the stackedstructure, as shown in FIG. 6B, a resist layer is formed overall on thesilicon oxide layer 94 and an opening portion is formed, by thephotolithography technique, in the resist layer at a positioncorresponding to a flat portion, parallel to the C-plane, in which anelectrode is to formed. A portion of the silicon oxide layer 94, locatedat the opening portion, is removed by RIE or wet etching using, forexample, a hydrofluoric acid-based etchant, to form a window portion 95having a shape corresponding to that of the opening portion in thesilicon oxide layer 94. The depth of the window portion 95 reaches thesurface of the silicon oxide layer 93 doped with Mg.

After formation of the window portion 95, a resist layer 96 for forminga p-side electrode, which has a window portion 96 d, is formed byphotolithography. The window portion 96 d is slightly wider than thewindow portion 95, so that part of the silicon oxide layer 94 and thesurface of the GaN layer 93 doped with Mg are exposed within the windowportion 96 d.

After the mask of the resist layer 96 and the silicon oxide layer 94 isformed, as shown in FIG. 6C, a p-side electrode material such asNi/Pt/Au or Ni(Pd)/Pt/Au is deposited via the window portion 96 d, toform a p-side electrode material layer 97. Since a height differenceequivalent to the total height of the resist layer 96 and the siliconoxide layer 94 lies between the top and the bottom of the window portion96 d, the film is thinned or not formed at the stepped portion of thewindow portion 96 d, whereby a p-side electrode 98 having a plug-likeshape with flanges on the upper side in cross section is formed in thewindow portion 95.

After the p-side electrode 98 is formed, as shown in FIG. 6D, the resistlayer 96 on the silicon oxide layer 94 is removed by using a solventsuch as acetone, to remove the p-side electrode material layer 97excluding the p-side electrode 98. Finally, an opening portion 100 isformed in such a manner as to reach the GaN layer 91 doped with Si, andan n-side electrode 99 is formed.

According to the above-described fabrication steps, even whenapproximately V-shaped valleys are formed by using stripe shapeddifference-in-height portions and a light emission region is formed in aflat portion, parallel to the C-plane, located between the valleys, theplug-like p-side electrode 98 can be formed on the flat portion in thelight emission region, to allow injection of a current in the lightemission region.

EXAMPLE SIX

As shown in FIG. 7, a multi-color light emitting device is fabricated,wherein two independent electrodes are provided to form along-wavelength light emission region and a short-wavelength lightemission region in accordance with an embodiment of the presentinvention.

A GaN layer 111 doped with silicon is formed on a principal plane (C+plane) of a sapphire substrate 110, and different-in-height portions areformed in a surface of the GaN layer 111. Subsequently, facet structureseach having inclined planes 112 inclined with respect to the substrateprincipal plane are formed by making use of the difference-in-heightportions. It is to be noted that in the fabrication process, respectivelayers are formed at about normal pressure, for example, about 740 Torr.A stacked structure of a GaN layer doped with Si, an InGaN layer, and aGaN layer 115 doped with Mg is formed so as to extend on a planeparallel to the inclined planes 112 and the C-plane. The InGaN layerheld between the two GaN layers acts as an active layer for emittinglight.

As shown in FIG. 7, an n-side electrode 116 is connected to the GaNlayer 111 doped with Si; and a p-side electrode is composed a p-sideelectrode 113 for a long-wavelength light emission region, which ispositioned at an approximately V-shaped valley formed by the inclinedplanes 112, and a p-side electrode 114 for a short-wavelength lightemission region, which is formed on a flat portion 117 between theadjacent approximately V-shaped valleys. An active layer formed at theapproximately V-shaped valley has a structure determined on the basis ofa composition and a thickness of the active layer, which structureallows emission of light having a long-wavelength, for example, emissionof light of green or red. In this regard, by injecting a current in theactive layer via the p-side electrode 113, it is possible to realizeemission of light having a long-wavelength, for example, emission oflight of green or red. An active layer formed on the flat portion 117between the adjacent approximately V-shaped valleys has a structuredetermined on the basis of a composition and a thickness of the activelayer, which structure allows emission of light having ashort-wavelength, for example, emission of light of blue. In thisregard, by injecting a current in the active layer via the p-sideelectrode 114, it is possible to realize emission of light having ashort-wavelength, for example, emission of light of blue.

Even if through-dislocations are propagated from the substrate, thepropagation of the through-dislocations is deflected by the inclinedplanes 112, to suppress occurrence of crystal defects, and since thefacet structures are not buried with the GaN layer, it is possible tofabricate the device for a relatively short time without increasing thenumber of processing steps. Further, light emission regions for emittinglight having different wavelengths can be formed on the same device bymaking use of a difference in composition and thickness between one ormore of the active layers formed on respective crystal planes of thefacet structure. In this regard, since the p-side electrodes 113 and 114are disposed on the upper and lower sides of the difference-in-heightportion, it is possible to form electrodes in micro-sized light emissionregions without occurrence of any problem of short-circuit.

EXAMPLE SEVEN

As shown in FIG. 8, a multi-color light emitting device in accordancewith an embodiment of the present invention is provided, is fabricated,wherein three independent electrodes are provided to form a red lightemission region, a green light emission region, and a blue lightemission region.

A GaN layer 121 doped with silicon is formed on a principal plane(C+plane) of a sapphire substrate 120, and different-in-height portionsare formed in a surface of the GaN layer 121. Subsequently, facetstructures each having inclined planes 122 inclined with respect to thesubstrate principal plane are formed by making use of thedifference-in-height portions. It is to be noted that in the fabricationprocess, respective layers are formed at about normal pressure, forexample, about 740 Torr. A stacked structure of a GaN layer doped withSi, an InGaN layer, and a GaN layer 125 doped with Mg is formed so as toextend on a plane parallel to the inclined planes 122 and the C-plane.The InGaN layer held between the two GaN layers acts as an active layerfor emitting light.

In an embodiment, to the semiconductor light emitting device of thepresent invention includes an n-side electrode 126 is connected to theGaN layer 121 doped with Si; and a p-side electrode is composed a p-sideelectrode 123 for a red light emission region, which is positioned at anapproximately V-shaped valley formed by the inclined planes 122, ap-side electrode 124 for a blue light emission region, which is formedon an upper flat portion 128 between the adjacent approximately V-shapedvalleys, and a p-side electrode 127 for a green light emission region,which is formed on a lower flat portion 129. An active layer formed atthe approximately V-shaped valley has a structure determined on thebasis of a composition and a thickness of the active layer, whichstructure allows emission of light of red. In this regard, by injectinga current in the active layer via the p-side electrode 123, it ispossible to realize emission of light of red. An active layer formed onthe upper flat portion 128 between the adjacent approximately V-shapedvalleys has a structure determined on the basis of a composition and athickness of the active layer, which structure allows emission of lightof blue. In this regard, by injecting a current in the active layer viathe p-side electrode 124, it is possible to realize emission of light ofblue. An active layer formed on the lower flat portion 129 has astructure determined on the basis of a composition and a thickness ofthe active layer, which structure allows emission of light of green, andaccordingly, by injecting a current in the active layer via the p-sideelectrode 127, it is possible to realize emission of light of green.

Even if through-dislocations are propagated from the substrate, thepropagation of the through-dislocations is deflected by the inclinedplanes 122, to suppress occurrence of crystal defects, and since thefacet structures are not buried with the GaN layer, it is possible tofabricate the device for a relatively short time without increasing thenumber of processing steps. Further, light emission regions for emittinglight having different wavelengths, particularly, light of red, blue,and green can be formed on the same device by making use of a differencein composition and thickness between one or more of the active layersformed on respective crystal planes of the facet structure. In thisregard, since the p-side electrodes 123, 124, and 127 are disposed atthree different points of the difference-in-height portion, that is,spatially separated from each other, it is possible to form electrodesin micro-sized light emission regions without occurrence of any problemof short-circuit.

FIG. 9 illustrates a state in which light is emitted from thesemiconductor light emitting device according to an embodiment of thepresent invention such that the semiconductor light emitting device canbe used, for example, as a light emitting diode. In this case, light 130is emerged from the back side of the device. The light 130 may be lightof a single color, multi-colors, or a mixture of colors. The colors oflight 130 can be controlled by applying currents to the p-sideelectrodes 123, 124, and 127. It should be appreciated that thesemiconductor light emitting device of the present invention can be in avariety of other suitable applications, including a semiconductor laserby forming a resonator end face at an end portion of the device. In theexample shown in FIG. 9, red laser light 133R, blue laser light 133B,and green laser light 133G are emerged from the end face of theresonator of the device. The end face of the resonator may be formed bycleavage.

EXAMPLE EIGHT

According to an embodiment of the present invention, a semiconductorlight emitting device capable of emitting white light can be fabricated,wherein as shown in FIG. 10, three independent electrodes are formed,and a common electrode for commonly driving the three electrodes isprovided.

A GaN layer 141 doped with silicon is formed on a principal plane(C+plane) of a sapphire substrate 140, and different-in-height portionsare formed in a surface of the GaN layer 141. Subsequently, facetstructures each having inclined planes 143 inclined with respect to thesubstrate principal plane are formed by making use of thedifference-in-height portions. These fabrication steps are the same asthose described in the previous embodiments. A stacked structure of aGaN layer doped with Si, an InGaN layer, and a GaN layer 142 doped withMg is formed so as to extend on a plane parallel to the inclined planes143 and the C-plane. The InGaN layer held between the two GaN layersacts as an active layer for emitting light.

According to an embodiment, the semiconductor of the present inventioncan include an n-side electrode 148 that is connected to the GaN layer141 doped with Si via an opening portion; and a p-side electrode is,like Example Seven, composed a p-side electrode 144 for a red lightemission region, which is positioned at an approximately V-shaped valleyformed by the inclined planes 143, a p-side electrode 145 for a bluelight emission region, which is formed on an upper flat portion betweenthe adjacent approximately V-shaped valleys, and a p-side electrode 146for a green light emission region, which is formed on a lower flatportion. In an embodiment, a common electrode 147 for commonly drivingthe p-side electrodes 144, 145 and 146 is formed. With the acid of thiscommon electrode 147, the device fabricated as the multi-color lightemitting device can be used as a light emitting device capable ofemitting white light.

Even if through-dislocations are propagated from the substrate, thepropagation of the through-dislocations is deflected by the inclinedplanes 143, to suppress occurrence of crystal defects, and since thefacet structures are not buried with the GaN layer, it is possible tofabricate the device for a relatively short time without increasing thenumber of processing steps. Further, according to an embodiment, sincelight emission regions for emitting light of red, blue, and green can beformed on the same device by making use of a difference in compositionand thickness between one or more of the active layers formed onrespective crystal planes of the facet structure, it is possible to emitwhite light by commonly driving the electrodes formed in the lightemission regions. The semiconductor light emitting device of the presentinvention, therefore, can be used as an illuminating unit or applied ina variety of other suitable applications.

EXAMPLE NINE

In an embodiment of the present invention, a semiconductor lightemitting device capable of emitting white light is fabricated, whereinas shown in FIG. 11, three independent electrodes are formed, and acommon electrode for commonly driving the three electrodes is provided.

A GaN layer 141 doped with silicon is formed on a principal plane (C+plane) of a sapphire substrate 140, and different-in-height portions areformed in a surface of the GaN layer 141. Subsequently, facet structureseach having inclined planes 143 inclined with respect to the substrateprincipal plane are formed by making use of the difference-in-heightportions. These fabrication steps are the same as those described in theprevious embodiments. A stacked structure of a GaN layer doped with Si,an InGaN layer, and a GaN layer 142 doped with Mg is formed so as toextend on a plane parallel to the inclined planes 143 and the C-plane.The InGaN layer held between the two GaN layers acts as an active layerfor emitting light.

In an embodiment, the semiconductor device of the present inventionincludes an n-side electrode 148 is connected to the GaN layer 141 dopedwith Si via an opening portion; and a p-side electrode is, like ExampleSeven, composed of a p-side electrode 144 for a red light emissionregion, which is positioned at an approximately V-shaped valley formedby the inclined planes 143, a p-side electrode 145 for a blue lightemission region, which is formed on an upper flat portion between theadjacent approximately V-shaped valleys, and a p-side electrode 146 afor a green light emission region, which is formed on the inclined plane143. In an embodiment, a common electrode 147 for commonly driving thep-side electrodes 144, 145 and 146 a is formed. With the acid of thiscommon electrode 147, the device fabricated as the multi-color lightemitting device can be used as a light emitting device capable ofemitting white light.

Even if through-dislocations are propagated from the substrate, thepropagation of the through-dislocations is deflected by the inclinedplanes 143, to suppress occurrence of crystal defects, and since thefacet structures are not buried with the GaN layer, it is possible tofabricate the device for a relatively short time without increasing thenumber of processing steps. Further, since light emission regions foremitting light of red, blue, and green can be formed on the same deviceby making use of a difference in composition and thickness between oneand another of the active layers formed on respective crystal planes ofthe facet structure, it is possible to emit white light by commonlydriving the electrodes formed in the light emission regions. Thesemiconductor light emitting according to an embodiment, therefore, canbe used as an illuminating unit or applied in other suitableapplications.

EXAMPLE TEN

In an embodiment, a semiconductor light emitting device of the presentinvention includes a structure shown in FIG. 12 as fabricated. A GaNlayer 151 doped with silicon is formed on a principal plane (C+ plane)of a sapphire substrate 150, and different-in-height portions 154 areformed in a surface of the GaN layer 151. Subsequently, facet structureseach having inclined planes inclined with respect to the substrateprincipal plane are formed by making use of the difference-in-heightportions 154. A stacked structure of a GaN layer 159 doped with Si(shown by a line in the figure), an InGaN layer 160, and a GaN layer 158doped with Mg (shown by a line in the figure) is formed so as to extendon a plane parallel to the inclined planes. The InGaN layer 160 heldbetween the two GaN layers acts as an active layer for emitting light.An n-side electrode 161 is connected to the GaN layer 151 doped with Si,and a p-side electrode 162 is connected to the GaN layer 158 doped withMg. The device emits light by supplying a current to the active layerbetween the p-side electrode 162 and the n-side electrode 161.

A current quantity adjusting circuit 170 is connected between the p-sideelectrode 162 and the n-side electrode 161 for adjusting a currentquantity so as to set an emission wavelength of the semiconductor lightemitting device to a desired wavelength. For example, the currentquantity adjusting circuit 170 can output a signal having a waveform (a)of cyclic pulses each having a short pulse width and a high peak valueand a waveform (b) of cyclic pulses each having a relatively long pulsewidth and a low peak value. When a signal having the waveform (a) issupplied between the p-side electrode 162 and the n-side electrode 161from the current quantity adjusting circuit 170, light of ashort-wavelength can be emitted from the device, and when a signalhaving the waveform (b) is supplied between the p-side electrode 162 andthe n-side electrode 161 from the current quantity adjusting circuit170, light of a long-wavelength can be emitted from the device. In thisway, the emission wavelength can be set to a desired wavelength bycontrolling a quantity of a current supplied to the device and awaveform of a signal supplied to the device.

As described above, the semiconductor light emitting device and themethod of fabricating the semiconductor light emitting device accordingto an embodiment of the present invention, even if through-dislocationsare propagated from the substrate, the propagation of thethrough-dislocations is deflected by the inclined planes, to suppressoccurrence of crystal defects. Further, since the facet structures arenot buried with the GaN layer, it is possible to fabricate the devicefor a relatively short time without increasing the number of processingsteps.

Since cladding layers and an active layer are formed on a planeextending in parallel to an inclined plane inclined with respect to thesubstrate principal plane, a portion having a good crystallinity can beused as a light emission region by making use of the increased number ofbonds of gallium to nitrogen at the inclined plane.

With the multi-color semiconductor light emitting device and the methodof fabricating the multi-color semiconductor light emitting deviceaccording to an embodiment of the present invention, light emissionregions for emitting light having different wavelengths, particularly,light of red, blue, and green can be formed on the same device by makinguse of a difference in composition and thickness between one or moreactive layers formed on respective crystal planes of a facet structure.Since respective electrodes, for example, p-side electrodes are disposedat three different points of the difference-in-height portion, that is,spatially separated from each other, it is possible to form electrodesin micro-sized light emission regions without occurrence of any problemof short-circuit.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A semiconductor light emitting device comprising: a substrate havinga surface that has a difference-in-height portion; a crystal growthlayer formed on the surface of the substrate wherein at least a portionof the crystal growth layer is oriented along an inclined plane withrespect to the surface of the substrate; and a first conductive layer,an active layer and a second conductive layer formed on the crystalgrowth layer in a stacked arrangement and oriented along the inclinedplane.
 2. The device of claim 1 wherein the substrate comprises awurtzite compound.
 3. The device of claim 1 wherein the wurtzitecompound forms a layer oriented along a principal place of the substrateand wherein the inclined plane is inclined with respect to the principalplane.
 4. The device of claim 1 wherein the inclined plane comprises atleast one of a S-plane and a {11-22} plane.
 5. The device of claim 1wherein the difference-in-height portion comprises a shape selected fromthe group consisting of a stripe shape, a rectangular shape, a roundshape, a triangular shape, a hexagonal shape and combinations thereof.6. The device of claim 1 wherein the crystal growth layer comprises ashape selected from the group consisting of a stripe shape, arectangular shape, a round shape, a triangular shape, a hexagonal shapeand combinations thereof.
 7. The device of claim 1 wherein the crystalgrowth layer further comprises a portion which is substantially parallelwith respect to a principal plane along which at least a portion of thesubstrate is oriented.
 8. The device of claim 1 wherein thesemiconductor light emitting device comprises a light emitting diodestructure.
 9. The device of claim 1 wherein the semiconductor lightemitting device comprises a semiconductor laser structure.
 10. Thedevice of claim 1 wherein the surface of the substrate is oriented alonga C-plane such that an end portion of the different-in-height portion isoriented perpendicular with respect to at least one of a <1-100>direction and a <11-20> direction and wherein the growth of the crystalgrowth layer depends on a shape of the difference-in-height portion. 11.The device of claim 1 wherein at least a portion of the crystal growthlayer forms a valley having a cross-section that is substantiallyV-shaped.
 12. The device of claim 11, wherein an electrode is formed onthe substantially V-shaped valley.
 13. A device of claim 1, wherein saidcrystal growth layer has a plurality of crystal growth layer portionsperpendicularly formed within a plane being approximately parallel to aprincipal plane of the substrate.
 14. The device of claim 1, wherein thecrystal growth layer comprises a GaN semiconductor.
 15. The device ofclaim 1, wherein the crystal growth layer is grown at a temperature ofabout 1100° C. or less.
 16. The device of claim 1, wherein the crystalgrowth layer is grown at pressure of about 100 Torr or more.
 17. Asemiconductor light emitting device comprising: a substrate comprising asubstrate layer composed of a wurtzite compound formed along a principalplane of the substrate wherein the layer includes a different-in-heightportion formed in a surface of the substrate layer; a crystal growthlayer formed on the surface of the substrate layer wherein at least aportion of the crystal growth layer is oriented along an inclined planethat is inclined with respect to the principal plane; a first conductivecladding layer, an active layer and a second conductive layer formed onthe crystal growth layer in a sequentially stacked arrangement orientedalong two or more planes of the crystal growth layer including theinclined plane such that one or more light emission regions are formed;and one or more electrodes separately formed in the light emissionregions.
 18. The device of claim 17, wherein the inclined planecomprises at least one of an S-plane and a {11-22} plane.
 19. The deviceof claim 17, wherein the principal plane comprises at least one of aC-plane and a {0001} plane.
 20. The device of claim 17, whereinwavelengths of two or more kinds of light emitted from the lightemission regions are different from each other.
 21. The device of claim20, wherein at least one of a composition and a thickness of the activelayer varies with respect to the light emission regions such that thewavelengths are different from each other.
 22. The device of claim 17,wherein the light emitting device has a light emitting diode structureallowing simultaneous emission of light associated with two or morecolors.
 23. The device of claim 17, wherein the light emitting devicehas a semiconductor laser structure allowing simultaneous emission oflight of two or more colors.
 24. The device of claim 17, wherein thesubstrate layer is oriented along a C-plane such that an end portion ofthe different-in-height portion is perpendicularly directed with respectto at least one of a <1-100> direction and a <11-20> direction andwherein the growth of the crystal growth layer depends on a shape of thedifferent-in-height portion.
 25. The device of claim 17, wherein atleast a portion of the crystal growth layer forms a valley having across-section that is approximately V-shaped.
 26. The device of claim25, wherein at least one of the electrodes is formed on theapproximately V-shaped valley.
 27. The device of claim 17, wherein thecrystal growth layer comprises a GaN semiconductor.
 28. The device ofclaim 17, wherein the crystal growth layer is grown at a temperature ofabout 1100° C. or less.
 29. The device of claim 17, wherein the crystalgrowth layer is grown at a pressure of about 100 Torr or more.
 30. Amethod of producing a semiconductor light emitting device, the methodcomprising the steps of: forming a wurtzite compound layer having asurface that has a difference-in-height portion; forming a crystalgrowth layer on the surface of the wurtzite compound layer wherein atleast a portion of the crystal growth layer is oriented along aninclined plane selected from the group consisting of an S-plane, a{11-22} plane and planes substantially equivalent thereto; and forming afirst conductive layer, an active layer and a second conductive layer ina sequential manner on the crystal growth layer such that the firstconductive layer, the active layer and the second conductive layer areoriented along the inclined plane.
 31. The method of claim 30, whereinthe semiconductor light emitting device is separated into a plurality oflight emission regions electrically independent from each other.
 32. Themethod claim 31, wherein an amount of current injected in the lightemission regions is capable of being adjusted to establish wavelengthsof light emitted from the light emission regions to a desired value. 33.The method of claim 30 further comprising the steps of: forming a resistlayer, and forming a specific pattern of an electrode layer by alift-off process.
 34. The method of claim 30 further comprising thesteps of: forming a resist layer having a window region, forming anelectrode layer to cover said resist layer including an inner region ofsaid window region, and removing said resist layer together with saidelectrode layer excluding an electrode portion formed on a bottom regionof the window region by a lift off process.
 35. The method of claim 30,wherein the crystal growth layer is grown at a temperature of about1100° C. or less.
 36. The method of claim 30, wherein the crystal growthlayer is grown at a pressure of about 100 Torr or more.